swift234

SILGen: Use vtable thunk abstraction for super_method instructions

The constant provided to the callee for super methods reference the
backing implementation, but the vtable entry may point to a thunk with
different abstraction when using mixed concrete and generic classes in
the hierarchy. The SIL devirtualizer expects super method references to
match what's in the vtable.

Also update the verifier for SuperMethodInst types - before it required
that the types be the same, but they may not be for the same reasons noted
above. Instead, do a similar check as for ClassMethodInst.

https://bugs.swift.org/browse/SR-134